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<div class="title">samples/cpp/lkdemo.cpp</div>  </div>
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<p>An example using the Lucas-Kanade optical flow algorithm</p>
<div class="fragment"><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dc2/modules_2video_2include_2opencv2_2video_2tracking_8hpp.html">opencv2/video/tracking.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../dc/d3d/videoio_8hpp.html">opencv2/videoio.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"><span class="preprocessor">#include &lt;ctype.h&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d8/dcc/namespacestd.html">std</a>;</div><div class="line"></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> help()</div><div class="line">{</div><div class="line">    <span class="comment">// print a welcome message, and the OpenCV version</span></div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nThis is a demo of Lukas-Kanade optical flow lkdemo(),\n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;Using OpenCV version &quot;</span> &lt;&lt; <a name="a0"></a><a class="code" href="../../da/dd7/core_2include_2opencv2_2core_2version_8hpp.html#a4f050efda432e041621b3af3df140adc">CV_VERSION</a> &lt;&lt; endl;</div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nIt uses camera by default, but you can provide a path to video as an argument.\n&quot;</span>;</div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nHot keys: \n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;\tESC - quit the program\n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;\tr - auto-initialize tracking\n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;\tc - delete all the points\n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;\tn - switch the \&quot;night\&quot; mode on/off\n&quot;</span></div><div class="line">            <span class="stringliteral">&quot;To add/remove a feature point click it\n&quot;</span> &lt;&lt; endl;</div><div class="line">}</div><div class="line"></div><div class="line"><a name="_a1"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point2f</a> point;</div><div class="line"><span class="keywordtype">bool</span> addRemovePt = <span class="keyword">false</span>;</div><div class="line"></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> onMouse( <span class="keywordtype">int</span> event, <span class="keywordtype">int</span> x, <span class="keywordtype">int</span> y, <span class="keywordtype">int</span> <span class="comment">/*flags*/</span>, <span class="keywordtype">void</span>* <span class="comment">/*param*/</span> )</div><div class="line">{</div><div class="line">    <span class="keywordflow">if</span>( event == <a name="a2"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#gga927593befdddc7e7013602bca9b079b0ad3419100fc2d7688c6dbe3da030fbfd9">EVENT_LBUTTONDOWN</a> )</div><div class="line">    {</div><div class="line">        point = <a name="a3"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>((<span class="keywordtype">float</span>)x, (<span class="keywordtype">float</span>)y);</div><div class="line">        addRemovePt = <span class="keyword">true</span>;</div><div class="line">    }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main( <span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv )</div><div class="line">{</div><div class="line">    <a name="_a4"></a><a class="code" href="../../d8/dfe/classcv_1_1VideoCapture.html">VideoCapture</a> cap;</div><div class="line">    <a name="_a5"></a><a class="code" href="../../d9/d5d/classcv_1_1TermCriteria.html">TermCriteria</a> termcrit(<a name="a6"></a><a class="code" href="../../d9/d5d/classcv_1_1TermCriteria.html#a56fecdc291ccaba8aad27d67ccf72c57aeb9da694ea67b3ef7d524521b580867d">TermCriteria::COUNT</a>|<a name="a7"></a><a class="code" href="../../d9/d5d/classcv_1_1TermCriteria.html#a56fecdc291ccaba8aad27d67ccf72c57a857609e73e7028e638d2ea649f3b45d5">TermCriteria::EPS</a>,20,0.03);</div><div class="line">    <a name="_a8"></a><a class="code" href="../../d6/d50/classcv_1_1Size__.html">Size</a> subPixWinSize(10,10), winSize(31,31);</div><div class="line"></div><div class="line">    <span class="keyword">const</span> <span class="keywordtype">int</span> MAX_COUNT = 500;</div><div class="line">    <span class="keywordtype">bool</span> needToInit = <span class="keyword">false</span>;</div><div class="line">    <span class="keywordtype">bool</span> nightMode = <span class="keyword">false</span>;</div><div class="line"></div><div class="line">    help();</div><div class="line">    <a name="_a9"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">cv::CommandLineParser</a> parser(argc, argv, <span class="stringliteral">&quot;{@input|0|}&quot;</span>);</div><div class="line">    <span class="keywordtype">string</span> input = parser.<a name="a10"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a190215863579a6d244dccfd261ee0224">get</a>&lt;<span class="keywordtype">string</span>&gt;(<span class="stringliteral">&quot;@input&quot;</span>);</div><div class="line"></div><div class="line">    <span class="keywordflow">if</span>( input.size() == 1 &amp;&amp; isdigit(input[0]) )</div><div class="line">        cap.<a name="a11"></a><a class="code" href="../../d8/dfe/classcv_1_1VideoCapture.html#a614a1702e15f42ede5100014ce7f48ed">open</a>(input[0] - <span class="charliteral">&#39;0&#39;</span>);</div><div class="line">    <span class="keywordflow">else</span></div><div class="line">        cap.<a class="code" href="../../d8/dfe/classcv_1_1VideoCapture.html#a614a1702e15f42ede5100014ce7f48ed">open</a>(input);</div><div class="line"></div><div class="line">    <span class="keywordflow">if</span>( !cap.<a name="a12"></a><a class="code" href="../../d8/dfe/classcv_1_1VideoCapture.html#a9d2ca36789e7fcfe7a7be3b328038585">isOpened</a>() )</div><div class="line">    {</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Could not initialize capturing...\n&quot;</span>;</div><div class="line">        <span class="keywordflow">return</span> 0;</div><div class="line">    }</div><div class="line"></div><div class="line">    <a name="a13"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>( <span class="stringliteral">&quot;LK Demo&quot;</span>, 1 );</div><div class="line">    <a name="a14"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga89e7806b0a616f6f1d502bd8c183ad3e">setMouseCallback</a>( <span class="stringliteral">&quot;LK Demo&quot;</span>, onMouse, 0 );</div><div class="line"></div><div class="line">    <a name="_a15"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> gray, prevGray, image, frame;</div><div class="line">    vector&lt;Point2f&gt; points[2];</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span>(;;)</div><div class="line">    {</div><div class="line">        cap &gt;&gt; frame;</div><div class="line">        <span class="keywordflow">if</span>( frame.empty() )</div><div class="line">            <span class="keywordflow">break</span>;</div><div class="line"></div><div class="line">        frame.<a name="a16"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#a33fd5d125b4c302b0c9aa86980791a77">copyTo</a>(image);</div><div class="line">        <a name="a17"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>(image, gray, <a name="a18"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a353a4b8db9040165db4dacb5bcefb6ea">COLOR_BGR2GRAY</a>);</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span>( nightMode )</div><div class="line">            image = <a name="a19"></a><a class="code" href="../../d1/da0/classcv_1_1Scalar__.html#ac1509a4b8454fe7fe29db069e13a2e6f">Scalar::all</a>(0);</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span>( needToInit )</div><div class="line">        {</div><div class="line">            <span class="comment">// automatic initialization</span></div><div class="line">            <a name="a20"></a><a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga1d6bb77486c8f92d79c8793ad995d541">goodFeaturesToTrack</a>(gray, points[1], MAX_COUNT, 0.01, 10, <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>(), 3, 3, 0, 0.04);</div><div class="line">            <a name="a21"></a><a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga354e0d7c86d0d9da75de9b9701a9a87e">cornerSubPix</a>(gray, points[1], subPixWinSize, <a name="a22"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga346f563897249351a34549137c8532a0">Size</a>(-1,-1), termcrit);</div><div class="line">            addRemovePt = <span class="keyword">false</span>;</div><div class="line">        }</div><div class="line">        <span class="keywordflow">else</span> <span class="keywordflow">if</span>( !points[0].empty() )</div><div class="line">        {</div><div class="line">            vector&lt;uchar&gt; status;</div><div class="line">            vector&lt;float&gt; err;</div><div class="line">            <span class="keywordflow">if</span>(prevGray.<a name="a23"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abbec3525a852e77998aba034813fded4">empty</a>())</div><div class="line">                gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#a33fd5d125b4c302b0c9aa86980791a77">copyTo</a>(prevGray);</div><div class="line">            <a name="a24"></a><a class="code" href="../../dc/d6b/group__video__track.html#ga473e4b886d0bcc6b65831eb88ed93323">calcOpticalFlowPyrLK</a>(prevGray, gray, points[0], points[1], status, err, winSize,</div><div class="line">                                 3, termcrit, 0, 0.001);</div><div class="line">            <span class="keywordtype">size_t</span> i, k;</div><div class="line">            <span class="keywordflow">for</span>( i = k = 0; i &lt; points[1].size(); i++ )</div><div class="line">            {</div><div class="line">                <span class="keywordflow">if</span>( addRemovePt )</div><div class="line">                {</div><div class="line">                    <span class="keywordflow">if</span>( <a name="a25"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga4e556cb8ad35a643a1ea66e035711bb9">norm</a>(point - points[1][i]) &lt;= 5 )</div><div class="line">                    {</div><div class="line">                        addRemovePt = <span class="keyword">false</span>;</div><div class="line">                        <span class="keywordflow">continue</span>;</div><div class="line">                    }</div><div class="line">                }</div><div class="line"></div><div class="line">                <span class="keywordflow">if</span>( !status[i] )</div><div class="line">                    <span class="keywordflow">continue</span>;</div><div class="line"></div><div class="line">                points[1][k++] = points[1][i];</div><div class="line">                <a name="a26"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#gaf10604b069374903dbd0f0488cb43670">circle</a>( image, points[1][i], 3, <a name="a27"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0,255,0), -1, 8);</div><div class="line">            }</div><div class="line">            points[1].resize(k);</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span>( addRemovePt &amp;&amp; points[1].<a name="a28"></a><a class="code" href="../../df/d5b/namespacecv_1_1gapi_1_1streaming.html#a0a915e69f4cc8284293e40fc9ffbf157">size</a>() &lt; (<span class="keywordtype">size_t</span>)MAX_COUNT )</div><div class="line">        {</div><div class="line">            vector&lt;Point2f&gt; tmp;</div><div class="line">            tmp.push_back(point);</div><div class="line">            <a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga354e0d7c86d0d9da75de9b9701a9a87e">cornerSubPix</a>( gray, tmp, winSize, <a class="code" href="../../dc/d84/group__core__basic.html#ga346f563897249351a34549137c8532a0">Size</a>(-1,-1), termcrit);</div><div class="line">            points[1].push_back(tmp[0]);</div><div class="line">            addRemovePt = <span class="keyword">false</span>;</div><div class="line">        }</div><div class="line"></div><div class="line">        needToInit = <span class="keyword">false</span>;</div><div class="line">        <a name="a29"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;LK Demo&quot;</span>, image);</div><div class="line"></div><div class="line">        <span class="keywordtype">char</span> c = (char)<a name="a30"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>(10);</div><div class="line">        <span class="keywordflow">if</span>( c == 27 )</div><div class="line">            <span class="keywordflow">break</span>;</div><div class="line">        <span class="keywordflow">switch</span>( c )</div><div class="line">        {</div><div class="line">        <span class="keywordflow">case</span> <span class="charliteral">&#39;r&#39;</span>:</div><div class="line">            needToInit = <span class="keyword">true</span>;</div><div class="line">            <span class="keywordflow">break</span>;</div><div class="line">        <span class="keywordflow">case</span> <span class="charliteral">&#39;c&#39;</span>:</div><div class="line">            points[0].clear();</div><div class="line">            points[1].clear();</div><div class="line">            <span class="keywordflow">break</span>;</div><div class="line">        <span class="keywordflow">case</span> <span class="charliteral">&#39;n&#39;</span>:</div><div class="line">            nightMode = !nightMode;</div><div class="line">            <span class="keywordflow">break</span>;</div><div class="line">        }</div><div class="line"></div><div class="line">        <a name="a31"></a><a class="code" href="../../d0/de1/group__core.html#gafbc8f513f40dc1b7c2d48ea6a5a81776">std::swap</a>(points[1], points[0]);</div><div class="line">        <a class="code" href="../../d0/de1/group__core.html#gafbc8f513f40dc1b7c2d48ea6a5a81776">cv::swap</a>(prevGray, gray);</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line">}</div></div><!-- fragment --> </div><!-- contents -->
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